Conventionally, in a standard automobile engine (for example, a gasoline engine), a throttle valve (intake-air throttle valve) is provided inside an intake air pipe, and an intake air quantity is adjusted by controlling a degree of opening of this throttle valve.
Incidentally, in winter and in other cases wherein an external air temperature is low, moisture contained in the intake air freezes (icing) in the vicinity of the throttle valve, and this throttle valve may become bonded through freezing to an inner surface of the intake air pipe (an inner surface of an intake air channel of a throttle body). Particularly during an idling operation wherein the degree of opening of the throttle valve is small, freezing of moisture between an outer peripheral edge of the throttle valve and an inner surface of the intake air pipe occurs more readily. In such a condition, the throttle valve becomes unable to operate correctly, causing driving of the engine to be obstructed.
In order to prevent or eliminate the above-mentioned freeze bonding of the throttle valve, a peripheral section of the throttle valve within the throttle body is heated using an engine coolant as disclosed in, for example, Patent Document 1 and Patent Document 2 below. More specifically, a channel for supplying the engine coolant is formed inside the throttle body, and by connecting this channel and a water jacket via piping, high temperature engine coolant is caused to flow to the peripheral section of the throttle valve, and consequently, freezing of the moisture inside the intake air channel can be prevented or ice frozen inside the intake air channel can be melted.
However, in a configuration wherein freeze bonding of the throttle valve is prevented or eliminated using the engine coolant as explained above, it is necessary for the engine coolant channel formed in the throttle body and the engine cooling system (water jacket) to be connected via piping, and it has been difficult to secure space for provision of this piping. Furthermore, as the above-mentioned prevention and elimination of freeze bonding will not be accomplished if the temperature of the engine coolant does not rise to a certain degree, heating of the peripheral section of the throttle valve prior to starting of the engine and sufficient heating of the peripheral section of the throttle valve during a short period of time after starting of the engine were not possible.
As a means of resolving these problems, heating of the peripheral section of the throttle valve using an electric heater and preventing or eliminating freeze bonding thereof has been proposed as disclosed in Patent Document 3 below.
Patent Document 1: JP H10-331621A
Patent Document 2: JP 2002-242706A
Patent Document 3: JP H10-26033A